This application claims the priority of German patent application number 196 43 054.2, the disclosure of which is expressly incorporated by reference herein.
The invention relates to a valve containing a Laval nozzle and a valve needle axially movable in the Laval nozzle.
A valve of this general type is known from in German patent application number DE 42 33 207 A1. The valve in that document is used as a vent valve for venting evacuated chambers. The inlet chamber that receives the valve needle foot, into which chamber the air used for venting purposes flows radially, is located upstream, directly adjacent to the entry plane of the Laval nozzle. The end of the Laval nozzle that faces the inlet chamber serves as a stroke-limiting stop surface for a matching stop bead on the valve needle foot.
German patent document DE 36 26 681 A1 relates to a valve for controlling the quantity of air and/or fuel in internal combustion engines, said valve being located in a corresponding intake air manifold. The valve comprises a Laval nozzle and a closing body engaging therein, said body having a conical shape with a base surface domed skirtwise and guided axially movably on a guide tube. The nozzle inlet area is defined by the closing body outer surface domed skirtwise and by a diaphragm with a concave shape surrounding said surface at a distance therefrom, and with an inlet chamber directly abutting said diaphragm, said chamber receiving the air or fuel flow drawn in radially or axially.
A regulating valve is known from German patent document DE 34 44 039 A1, including a Laval nozzle and a valve needle axially movably engaging the Laval nozzle. The valve needle is surrounded in a central section by a tubular valve housing with a space therebetween, with guide vanes being provided in the annular gap formed thereby in order to guide and direct the gas flow passing through. On the inlet side, a supply line connects to the tubular valve housing, said line having a slightly smaller inside cross section than the tubular valve housing and being bent outward diagonally from the axial direction in a rounded arc toward the inlet opening. The foot area of the valve needle, which runs axially in a straight line, passes through a throughput opening provided in the feed tube, with a guide bushing being installed in this through opening and serving for axially movable guidance of the valve needle.
The known property of a Laval nozzle, namely that the pressure ratios on the outlet side do not influence the inlet area, is utilized in a fuel injection device in German patent document DE 41 00 086 A1 for an internal combustion engine. The Laval nozzle is located between a fuel outlet opening and a mixture outlet opening located downstream therefrom. The Laval nozzle permits good preparation of the fuel-air mixture without a high fuel injection pressure being required.
For metering process gases supplied, metering valves are known in process technology in the form of pulse-width controlled 2/2-way valves, needle valves with an adjusting device, or proportionally operating solenoid valves. For precise metering of volumes of gas into a process reactor with a fluctuating internal pressure, a costly pressure-regulating system must usually be installed in order to maintain the desired metering accuracy. In addition, in these conventional valves, a costly regulating circuit with corresponding sensorics is often required. The mass-flow devices used for this purpose theoretically exhibit a certain amount of inertia that limits the speed with which metering changes can be made.
The invention has as the technical goal to be achieved the provision of a valve of the species recited at the outset with a flow guidance that is comparatively insensitive in terms of pressure fluctuations, as well as an advantageous application for such a valve.
This and other needs have been met according to the present invention by providing a valve comprising: a Laval nozzle; a valve needle axially movable in said Laval nozzle; an inlet chamber receiving a foot of said valve needle; an inlet opening communicating with said chamber, said inlet opening extending radially, said inlet chamber being spaced axially from an inlet plane of said Laval nozzle by a flow channel located therebetween, said flow channel being delimited by said valve needle and by a valve housing section that surrounds the valve needle and guides the valve needle axially.
This and other needs have also been met according to the present invention by providing a valve comprising: a housing defining an inlet chamber and a flow channel communicating with each other; a Laval nozzle arranged in said housing and defining an axial direction, said Laval nozzle defining a convergent flow cross-section communicating with said flow channel and a divergent flow cross-section adjacent said convergent flow cross-section at a narrowest cross-section; and a valve needle supported in said housing, said valve needle having a portion with a cross-section which varies in said axial direction, said valve needle being arranged such that said portion is axially movable in said Laval nozzle in order to vary a cross-sectional area of an opening defined between said portion and said narrowest cross-section of said Laval nozzle.
This and other needs have also been met according to the present invention by providing a method of metering a fluid, comprising the steps of: forming a housing to define an inlet chamber and a flow channel communicating with each other; arranging a Laval nozzle in an axial direction in said housing such that said Laval nozzle is in communication with and is downstream of said flow channel; arranging a valve needle to be axially movably supported by said housing such that a portion of said valve needle with a cross-section which varies in said axial direction is movable in said Laval nozzle; and ontrolling an axial position of said valve needle relative to said Laval nozzle in order to vary a cross-sectional area of an opening defined between said portion of said valve needle and said Laval nozzle.
In a valve according to a preferred embodiment of the present invention, the inlet chamber in which one or more radially extending inlet openings terminate is spaced axially from the inlet plane of the Laval nozzle by a flow channel located therebetween, said channel being limited radially on the inside by the valve needle and radially on the outside by a valve housing section that surrounds the valve needle with a corresponding space therebetween. Accordingly, the deflection of the radially guided flow into the axial flow in the Laval nozzle area takes place at a distance in front of the nozzle inlet that corresponds to the length of the flow channel. The flow guided through the valve thus travels over the length of this flow channel before reaching the narrowest throughput cross section in the Laval nozzle area in the axial direction, in which direction it also passes through the Laval nozzle. As a result, in the vicinity of the narrowest throughput cross section of the Laval nozzle, the critical nozzle flow at that point (M=1) can be adjusted to remain stable without pressure fluctuations, especially those of the backpressure that prevails at the outlet side of the Laval nozzle, significantly disturbing this stable through flow.
The spacing of the flow deflection area in the valve according to the invention, in other words in the inlet chamber, from the inlet plane of the Laval nozzle also creates a situation in which flow deflection takes place in a zone in which the flow rate is still significantly less than in the inlet area of the Laval nozzle. As a result, the flow deflection losses can be kept low which in turn means that the valve can be used to provide the desired, defined flow ratios over a relatively wide usable operating range of the ratio of the backpressure to the forepressure, in other words of the pressure at the nozzle outlet to the pressure at the nozzle inlet.
A valve according to a preferred embodiment of the present invention exhibits favorable through flow properties as well as a valve needle travel limitation that is defined by stop surfaces located outside the Laval nozzle so that the Laval nozzle surfaces are not subjected to corresponding impact forces.
According to certain preferred embodiments of the present invention, a sleeve is placed in the valve housing. The sleeve serves as a guide for the axially movable valve needle guided through the sleeve and also defines one or more recesses extending axially. These recesses in this area form the corresponding portion of the flow channel located therebetween.
The valve according to certain the present invention may be used as a metering valve for metering a process gas for a reaction process in a motor vehicle operated on fuel cells. Very exact metering of the process gas in question can be accomplished with the valve, at comparatively low cost, which is of great significance for the corresponding reactions in the fuel cells themselves and/or the reactors connected upstream from the cells, for example reformation reactors for obtaining hydrogen. The valve design according to the invention therefore makes it possible in an economical fashion and without active sensorics and regulating circuits, to adjust the desired mass flow largely independently of pressure fluctuations.
The invention therefore provides an apparatus and a method which, at a constant forepressure and flow pressure, measure mass flow as a linear function of the cross-section of the opening between the narrowest cross-section of the Laval nozzle and the needle, which cross-section of the opening is adjustable by axial movement of the needle via the linear actuator to control the mass flow.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.